We propose to study the mechanisms whereby eukaryotic sigma-like factors (S factors) from calf thymus promote initiation of RNA synthesis by homologous RNA polymerase II. This involves three aspects of research. A. The subunit structures of S factors will be defined and compared with each other and to the small subunits of RNA polymerase II. If the data indicate size identity, interconversion of the various forms of the factor will be examined using cAMP- and cGMP dependent protein kinases. B. The role of S factors in binary complex formation, strand selection, initiation, elongation and termination during transcription of SV40 DNA (Form I) by calf thymus RNA polymerase II will be examined. C. The role of S factors in the reconstitution of RNA polymerase II subunits will be examined to ascertain whether S factors act as subunit assembly factors.